JPS62103587A - Laser radar - Google Patents

Abstract

PURPOSE:To enable the use of a narrow transmission band filter without controlling the temperature of a semiconductor laser by changing the angle of inclination of an interference filter when the oscillation wavelength of a semiconductor laser changes by temperature so that the oscillation wavelength enters a center wavelength area. CONSTITUTION:At the start of operation of a semiconductor laser 1, the angle theta0 of inclination of an incident surface is determined to ensure that the center wavelength of an interference filter 5 will equal the initial oscillation wavelength lambda0. The angle theta0 is initialized. Then, the angle of incidence of the incident plane is tilted 8 by so that center wavelength of the filter 5 shifts by + or -DELTAtheta from the oscillation wavelength lambda0 and a reference light 11 is received 6. The output value of a detector 6 at + or -DELTAthetais discriminated 7 to be large or small and according to the judgement, which direction the oscillation wavelength is determined. Angle information which can provide the angle of inclination of incident surface to make both output values equal is outputted to an adjustor 8. The center wavelength of the filter 5 after the change should be matched. AS a result, a light receiving section 9 can a reflected laser light 13 with the optimum intensity regardless of changes in the oscillation wavelength of the laser 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a laser radar device using a semiconductor laser.

(Prior Art) In a laser radar device using a conventional semiconductor laser, the oscillation wavelength of the semiconductor laser changes depending on the temperature, and the wavelength change range is as wide as, for example, 500. A filter with a transmission band that includes the changing wavelength range is used.

(Problem to be solved by the invention) However, in conventional laser radar devices, it is necessary to widen the transmission band of the filter for removing background light, so the effect of removing background light cannot be expected to be very high, and effective measurement is difficult. The problem is that this can only be done at night when there is little background light.

To solve this problem, it is possible to use a filter with a narrow transmission band, but to do so, it is necessary to control the temperature of the semiconductor laser so that the operating temperature of the semiconductor laser is at the required value, and to suppress changes in the oscillation wavelength due to temperature. There is. but,
This poses a problem in that the device becomes larger and more complex, leading to increased costs. An object of the present invention is to enable the use of a narrow transmission band filter without temperature control of a semiconductor laser.

(Means for Solving the Problems) In order to achieve the above object, a laser radar device according to the present invention has the following configuration.

That is, a semiconductor laser that generates a laser beam: A part of the projected laser beam from the semiconductor laser is transmitted as a reference beam, and the reflected laser beam of the projected laser beam is parallel to the transmitted optical path of the reference beam. an interference filter that transmits the laser beam; angle adjusting means that changes the inclination angle of the interference filter to change the angle of incidence of the laser beam on the interference filter;
A control means for receiving the transmitted reference light of the interference filter and controlling the angle adjusting means so that the amount of transmission of the transmitted reference light becomes the maximum amount of transmission of the interference filter.

(Function) Next, the function of the laser radar device of the present invention configured as described above will be explained. Laser light generated by the semiconductor laser is projected onto a target, and reflected laser light from the target is introduced into a light receiving section.

At this time, the interference filter is arranged so that a part of the projected laser light from the semiconductor laser is transmitted as a reference light, and the reflected laser light of the projected laser light is transmitted parallel to the transmitted optical path of the reference light. Therefore, the reflected laser light is introduced into the light receiving section via the interference filter. On the other hand, the transmitted reference light of the interference filter is input to the control means.

The control means receives the transmitted reference light and controls the angle adjustment means so that the amount of transmission of the transmitted reference light becomes the maximum amount of transmission of the interference filter. Thereby, the angle adjusting means changes the inclination angle of the interference filter, and changes the incident angle of the reference beam and the reflected laser beam.

It is known that the center wavelength that provides the maximum transmission amount of an interference filter changes depending on the angle of incidence, and that as the angle of incidence increases, for example, the center wavelength shifts to the shorter wavelength side, and the present invention utilizes this. It is.

In other words, when the oscillation wavelength of the semiconductor laser changes and deviates from the center wavelength of the interference filter, the control means and angle adjustment means change the inclination angle of the interference filter so that the oscillation wavelength of the semiconductor laser is in the center wavelength region. The light receiving section is adjusted so that the amount of transmission always near the maximum is obtained.

Since the interference filter is a filter with a narrow transmission band, the light receiving section receives reflected laser light from which background light has been removed.

As described above, according to the present invention, when the oscillation wavelength of the semiconductor laser changes due to temperature, the inclination angle of the interference filter is changed so that the oscillation wavelength is in the center wavelength region, so the temperature of the semiconductor laser can be controlled. At least a narrow transmission band filter can be used, and a laser radar device with a large background light removal effect can be provided at low cost.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1st
The figure shows a laser radar device according to an embodiment of the present invention,
This laser radar device projects a laser beam generated by a semiconductor laser 1 onto a target (not shown) by a transmitting optical system 2, and introduces the reflected laser beam from the target into a light receiving section 9 by a receiving optical system 10. In this system, a beam sublitter 3 extracts a part of the laser beam projected through the transmitting optical system 2 as a reference beam 11, and a beam subritter 3 extracts a part of the laser beam projected through the transmitting optical system 2 as a reference beam 11, and a receiving optical axis 12 of the receiving optical system 1o transfers the reference beam 11 extracted by the beam sublitter 3. a reflector 4 that parallelizes and reflects the light, a detector 6 into which the reference light 11 reflected by the reflector 4 is input, a discriminator 7 that receives the detection output of the detector 6, and a reflector 4 and the detector 6. and between the receiving optical system 10 and the light-receiving section 9, there is an interference filter 5 that blocks each optical path and is interposed so that its incident surface can tilt and rotate around its center as a fulcrum, and a control signal (angle information) from the discriminator 7. ) and an angle adjuster 8 that changes the angle of inclination of the incident surface of the interference filter 5 in response to the angle of incidence.

Since the reference light 11 reflected by the reflecting mirror 4 and the reflected laser light 13 passed through the receiving optical system 10 and converged are transmitted in parallel to the interference filter 5, even if the inclination angle of the incident surface changes, the reference light 11 will not change. The incident angle and the incident angle of the reflected laser beam 13 change at the same angle.

The angle adjuster 8 receives a command from the discriminator 7 to control the inclination of the incident surface as described later, and changing the inclination angle of the incident surface means changing the incident angle of the incident light. The angle of incidence of the incident light and the center wavelength of the interference filter 5 are expressed by the following formula (1
).

Here, λ0 is the center wavelength when the incident angle θ is θ=O°, that is, normal incidence, λ0 is the center wavelength at the incident angle θ, and n is the refractive index of the interference filter 5.

That is, the center wavelength of the interference filter 5 can be changed by changing the angle of incidence. For example, as shown in FIG. 2, when the angle of incidence θ of the interference filter 5 is increased, the center wavelength shifts to the shorter wavelength side.

As is clear from FIG. 2, the transmission characteristic is a narrow band characteristic, with the center wavelength λ. Transmission characteristics and center wavelength λθ
The transmittance characteristics in are the same and have a simple parallel displacement relationship. From this, it can be seen that by changing the angle of incidence on the interference filter 5, the center wavelength can be matched to the oscillation wavelength of the semiconductor laser 1. Specifically, the aim is to obtain the maximum amount of transmission.

The detector 6 and the discriminator 7 constitute a control means. The detector 6 receives the reference light 11 that has passed through the interference filter 5, and outputs the received light intensity value to the discriminator 7. The discriminator 7 determines the center wavelength of the interference filter 5 and the semiconductor laser 1 from the input received light intensity value. detects the deviation from the oscillation wavelength, and outputs angle information to the angle adjuster 8 according to the amount of deviation. The angle adjuster 8 appropriately tilts the entrance surface of the interference filter 5 based on this angle information.

As a result, the light receiving section 9 can always stably receive the reflected laser light 13 having an optimum intensity value even if the oscillation wavelength of the semiconductor laser 1 changes. Since the interference filter 5 has narrow transmission band characteristics, it has an excellent background light removal effect and enables effective measurement even in broad daylight.

Next, FIG. 3 shows the principle of incident angle control, which will be explained below with reference to the same figure.

First, at the beginning of the operation of the semiconductor laser 1, its initial oscillation wavelength λ. Find the angle θ0 of the inclination of the plane of incidence that gives the angle of incidence at which the center wavelength of the interference filter 5 is equal to the angle θ.

Initialize to .

Next, the angle adjuster 8 is used to shift the center wavelength of the interference filter 5 by ±Δ^ from the oscillation wavelength λ0 (see Fig. 3).
a)) Tilt the inclination angle of the incident surface by ±Δθ (Figure 3 (a)
), the reference light 11 is received by the detector 6.

Then, the discriminator 7 determines the magnitude relationship between the output value of the detector 6 at θ0+Δθ and the output value at θ0−Δθ, and if they are equal (FIG. 3(b)), the inclination angle of the incident surface is θ.

+Δθ and θ. -Δθ is output to the angle adjuster 8, and the inclination angle of the incident plane is set to θ0+Δθ and θ0−Δθ.
(Fig. 3 (a)), while the discriminator 7
If the front output values of the detector 6 are not equal, the direction of change of the oscillation wavelength is determined according to the magnitude relationship, and the angle information that gives the inclination angle of the incidence plane where the front output values are equal is sent to the angle detector 8.
The center wavelength of the interference filter 5 is made to match the changed oscillation wavelength.

For example, the inclination angle of the plane of incidence is θ0+Δθ and θ. When the oscillation wavelength of the semiconductor laser 1 is repeatedly set to -Δθ (FIG. 3 (c)), the oscillation wavelength of the semiconductor laser 1 becomes λ. 3(C)), the output value of the detector 6 is the inclination angle θ when the inclination angle is θ0−Δθ. It becomes larger than +Δθ.

As a result, the discriminator 7 determines that the oscillation wavelength has shifted to the one Δθ side and instructs the angle adjuster 8 to further tilt -Δθ, so the interference filter 5 adjusts the tilt angle θ0 and the tilt angle θ. -2
Δθ (Fig. 3 (c) and (e)), and the output value at the inclination angle θ0 of the detector 6 and the inclination angle θ
If the output values at o2Δθ are equal (Fig. 3 (f)
), the interference filter 5 continues to be set at the inclination angle of θ0 and θO−2Δθ (Fig. 3 (c)). On the other hand, if the output value at the inclination angle θo2Δθ is large among the previous output values of the detector 6, The discriminator 7 gives an instruction to the angle adjuster 8 to further tilt the interference filter 5 by −Δθ, and sets the tilt angle to θ0−Δθ.
and θ-3Δθ, and repeat the above-mentioned operation.

The above adjustment operation is performed at predetermined time intervals, and the discriminator 7
Once the values of both inclination angles at which the re-input values are equal are determined, the inclination angle that gives the maximum amount of transmission is determined, and the interference filter 5
Set to that angle and prepare for normal measurement.

(Effects of the Invention) As detailed above, according to the present invention, when the oscillation wavelength of the semiconductor laser changes due to temperature, the inclination angle of the interference filter is changed so that the oscillation wavelength is in the center wavelength region. , a narrow transmission band filter can be used without temperature control of the semiconductor laser, and a laser radar device with a large background light removal effect can be provided at low cost.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a laser radar device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between the incident angle and transmission characteristics of the interference filter, and Fig. 3 is the incident angle of the interference filter. It is an explanatory diagram explaining the principle of control. 1...Semiconductor laser, 2...Transmission optical system, 3...Beam splitter, 4...
Reflector, 5...Interference filter, 6...
・Detector, 7... Discriminator, 8...
Angle adjuster, 9... Light receiving section, 10...
・Reception optical system, 11...Reference light, 12...
...Receiving optical axis, 13...Reflected laser beam. Agent Patent Attorney Yoshi Yahata Hiroki Akira's Laser Laser 1. Figure 1 λQ λ0 Awesome Side Chikucho Interference Sulf 0 Incident A and Desire Full Situation)! Figure 2

Claims (1)

[Claims] a semiconductor laser that generates a laser beam; a portion of the projected laser beam from the semiconductor laser is transmitted as a reference beam, and a reflected laser beam of the projected laser beam is transmitted parallel to the transmission optical path of the reference beam; an interference filter; an angle adjusting means for changing the inclination angle of the interference filter in order to change the angle of incidence of the laser beam on the interference filter; A laser radar device comprising: control means for controlling the angle adjustment means so that the amount of transmission through the interference filter is the maximum.